Bob Garon — the 63-year-old gay Vietnam veteran who confronted Mitt Romney over gay marriage in New Hampshire on Monday — appeared on MSNBC’s Hardball with Chris Matthews this evening and challenged the former governor’s understanding of the Constitution. Romney, who supports a federal constitutional amendment outlawing same-sex marriage, had told Garon that “at the time the Constitution was written, it was pretty clear that marriage was between a man and a woman.” Garon said he was “dumbfounded” by Romney’s interpretation of the founding document:

MATTHEWS: Most people recognize that the Constitution has taken different meanings over the years because times have changed. I mean, there is no reference to an air force, for instance, in the Constitution….Were you surprised he took that sort of old, conservative argument, oh, that’s not the way Franklin looked at it? And by the way, we have no idea how they actually looked at it. What did you make of that?

GARON: Well, I was very surprised. First, I’m not a professor of the Constitution. I didn’t know he was either. I didn’t know the Constitution makes it clear what a marriage was between a man or a woman. There is nowhere in the Constitution that I can remember that it says anything about that and here is a man that plans to be in the White House and apparently he doesn’t know about the Constitution either. I was dumbfounded. I just don’t know where he came up with that kind of information.

Watch it:

While running for Senate in 1994, Romney himself argued that same-sex marriage is “a state issue as you know – the authorization of marriage on a same-sex basis falls under state jurisdiction.”